Utilization of petroleum refinery gas



E.'B. HJERPE ETAL l UTILIZATION OF PETROLEUM REFINERY GAS' Dec: 24,1940.

Filed May 7, 193e NNJOOU MzSM Q21 MIMJL lkw eifpes 2 use,

.vt/fiamma v .f www* Patented Dec. 24, i

UNITED STATES PATENT OFFICE Y n 2,226,461 e e 4 U'rI'LIzA'rIoN orPETnoLEUM REFINERY ons, A

. Eric B. Hjerpe, Port Arthur, Tex. and William A. Gruse, Wilkinsburg,Pa., assigner: to Gulf Oil Corporation, Pittsburgh, Pa., acorporation ofPennsylvania Application May '1. 193e, sei-iai no. 78,480

e 1 claim. (ci. zoo-ssa) This application is in part a continuation ofvour application Serial No. 613,774, illed May 26,

1932, now U. S. Patent No. 2,099,480.

The invention covered by this continuation-inpart application relates tothe utilization of pevtroleum refinery gas, and comprises a continuousprocess wherein renery gas containing methane,

. ethylene, ethane. propylene, propane, butylene,

butane, pentanes and higher boiling constituents, lo 1s stripped yof itscontained gasoline vapors (pentanes and higher boiling components); theresidue is next strippedof methane for deposition as desired; and theresidue from the last mentioned separation is further subjected tosuccessive fractionation for isolation of cuts containing individualoleilns such as ethylene, propylene and butyle ene; the charging stockfor a polymerization or gas conversion operation conducted for thepurpose of producing motor fuel.

More specifically, this invention provides a continuous process whereinuncondensed gas from the customary water-cooled condensers of petroleumcracking stills and/or coke stills and/or steam stills (said gascomprising methane. 25* ethylene, ethane, propylene, propane, butylene,

butane and higher boiling components) is subjected to compression and/orabsorption steps to liquefy and thereby separate and remove higherboiling constituents, leaving a residue of stripped 8 refinery gas. Thisstripped reilnery gas is chilled to a temperature sumcient to liquefyall components (higher boiling than methane and is introduced into atower and the methane fractionated out, the necessary chilling of thegas being eiectas ed by expanding it through an expansion valve aftercompressing it to the necessary degree and cooling it with water. Theliquid residue from lthe last mentioned tower is expanded into thesecond tower and the ethylene and ethane are similarly fractionated out;the liquid residue of the last mentioned separation, now freed .ofethylene, ethane and methane. is expanded into a fractionating tower andthe propylene and propane are fractionated out from residual butyleneand butane. e l

In particulanour invention relates to a method of fractionating gases ofthe character indicated, in which the gases after fractionation thereof,are passedthrough a series of fractionating steps in which constituentsor fractions of successively higher boiling points are removed, residualliquid from anyone of the aforesaid'towers beingemployed to assist inthe fractionation and sep?- aration taking place in a preceding'tower;

,. ,u v In order that our invention maybe clearly-.set

forth and understood, we now describe, with reference to the drawingaccompanying and forming a part of this specification, a preferredmanner in which our invention may be practiced andem ployed. Y 5 In thedrawing the single figure is a more or. less diagrammatic view ofapparatus for carrying out our invention arranged primarily as a ilowsheet.

Referring to the drawing, the numeral I indicates a stream of chargingstock to a conventional cracking still comprising a cracking coil 2,separating and dephlegmating tower 3, condenser l, and separator 5.These elements do not constitute a portion of this invention but areincluded4 for clarity of presentation. After condensa- 15 tion of`cracked distillate in the condenser 4 the distillate is separated fromaccompanyingiincondensed gasin separator 5. This gas, conducted awaythrough line 8, is raw material used in the process which constitutesour invention. Other raw material for our process is the correspondinguncondensed gas from petroleum ooking stills, lubricating stills, andsteam stills. Any one of these gases alone or any mixture of them isacceptable raw material and this raw materialwill 25- hereinafter bereferred to as still gas', or petroleum renery gas.

As a preliminarystep, the gas is first stripped of pentanes and allhigher boiling constituents. Some butane and butyiene may be removed atthis point, if it is ldesired to retain this mate, rial as suchin thecracked gasoline. This separation may be effected in various ways and wehave found compressionr and absorption methods very satisfactory, withsubsequent controlled u fractionation ofthe absorbed material.Absorption is-most effective when we maintain a'superatmosphericpressure of the order of 250 pounds or 300 pounds in theabsorber. 'I'hecompression can be effected in two stages as shown in the o drawing,with recooling of the gas after each compression stage. This compressionandy subsequent cooling will liquefy some of the' higher boilingconstituents oi the gas and so a separator is placed 'in the line whichconducts the cooled gas from one compression stage to anothercompressor. Liquefled material removed from this separator is termedcompression gasoline. drawing depicts two-stage compression withcompressors 1 and in, followed by recooling in coolers o 8 and- Ilrespectivelyf and removal of compresarator 9 through line I3. Aftercompression to u gas, leaves the absorber through line I5.

dissolved constituents of the gas, leaves the bottom of absorber l2through line I6 and is introduced through line I8 into a tower I9 wherethe absorbed constituents of the gas are distilled off and fractionated.Tower I9 is preferably opervated under a superatmospheric ,pressure and1 should its pressure not be suiciently below that Per cent Methane 45'Ethylene 5 Ethane 20 L Propylene I 8 Propane 15 Butylene 3 Butane 4 ofthe absorber to cause the necessary iiow through lines I6 and I8, a pumpl1 can be inserted in the line to effect the transfer of the liquid.Heat for distilling the absorbed constituents of the gas out of theabsorbent oil in tower I9 is provided by a closed steam coil orequivalent heating means in the lower portion of the tower. The upperportion of tower I9 is designed to ei'- fect clean fractionation oftheabsorbed material from the absorbent and the so-fractionated vaporsfromtower I9 pass to, andare condensed by, condenser 20. The eii'iuent ofthe condenser passes to gas separator 2I where any unliquefledcomponents of the gas are separated from the liquefied components. Thecondenser and gas separator 2| are maintained under the same pressureand the pressure and temperature of the condenser are chosen to assureliquefaction of normally liquid constituents without liquefaction ofnormally gaseous constituents, for example, propane and propylene. Anyhigher boiling fractions of the refinery gas which are liqueed incondenser 20 and separated from accompanying gas in separator 2l areconducted away through line 22. 'I'hat portion of the petroleum refinerygas which passes through condenser 20 without being liquefied thereinpassed out of the top of gas separator 2| through line 23. This linejoins line I 5, previously described, and the combined stream is termedstripped refinery gas. This stripped refinery gas contains butylene andbutane and all of the lower boiling constituents of the pertoleumrefinery gas. The relative proportions of the various constituents varywidely according to the kind of oil from which it originates, the kindof still in which it is produced, the temperature, pressure, and otherconditions attending its creation, and the condensation of accompanyingvapors in the still condenser (condenser 4 or its equivalent). Onetypical analysis of the stripped refinery gas-insofar as any analysiscould be termed typical--was the following, observed in operation of theprocess herein described and claimed:

Our next step is to fractionate out the methane. We do this byintroducing the `stripped reiinery gas at a sufficiently low temperatureinto a fractionatlng tower and the low temperature is obtained byself-coolingr 'incident to expansion' through an expansion valve or workengine. Further details follow. 'Ihe stripped refinery gas in line I5 iscompressed to whatever degree is necessary to effect that cooling at theexpansion valve which is requisite for liquefaction at tower pressure ofall constituents of the gas which boil at higher temperatures thanmethane. The tower pressure is advantageously chosen to permit furtherpressure drop in subsequent fractionating steps and yet maintainsuitable'worklng pressure at the last fractionating step. The

methane is fractionated out ln the tower 35 and in our practice of theinvention we have found a pressure of 500 pounds per square inch aboveatmospheric, before expansion, to be suitable for a gas such as the onewhich an analysis is shown above, and a pressure of seven atmosphereswithin the tower to be quite satisfactory. This pressure is generated bycompressor 24 and the heat generated in compression is removed from thegas by a cooler 25. The compressed land recooled gas is then incondition for chilling by expansion, for introduction into the towerl at33 and for fractionation therein. Expansion and consequent cooling iseffected at expansion valve 3l. Maincontent of the gas with a tower headtemperature of minus 140 C. and the remainder of the gas leaves the baseof the tower in liquid form at a temperature of minus 60 C. Thefractionation in the tower is more easily controllable if we have achilling means in the tower head and a warming means in the tower base.These are readily provided for by closed coils 21 and 32 in the' towerbase and head, respectively, and bypass connections in the incoming gasline, to admit of circulating this gas therethrough in such quantity as'is necessary to obtain the required control. Three valves 28 are shownfor permitting the use of regulated amounts of the unexpanded gas forcontrolling the temperature of the tower base and similar by-passconnection and valves are provided to permit the use of regulatedamounts of the expanded gas for controlling the temperature of the towerhead. 'Ihe by- Pass connection and valves 28 have been illustratedin\c,onnection with coil 21, their similar arrangement in connectionwith head coil 32 has been yomitted from the drawing for simplicity ofillustration. These same remarks apply as to the head coils in towers 40and 15, each of which is.

therewith through a. pierced diaphragm 36. The.

methane nnally ows away through line 31 for utilization.

The liquid residue leaves tower 35 through line 34 and comprisesethylene, ethane, propylene. propane, butylene and butane. This liquidis discharged into tower 40 at 42 for fractionation of ethylene andethane from the propylene, propane, butylene. and butane. Tower 40 maybe provided with coils 33 and 39 ior assisting in controlling the headand base temperatures thereof, and these coils are connected with line3l in by-pass arrangement and sequence as already fully described inconnection with coils 2 1 assess? j Y and. 32. A pressure of`six-atmospheres is maintained in'tower 40 and the ethylene and ethaneleave the top of the tower through line 4C at a temperature of minus 50C., while the propylene,

propane, butylene, and butane leave the base of the tower .through line`43 at a temperature of minus C.

A mixture of propylene, propane, butylene, and

i butane is removed from the base of tower 40 through line 43 under apressure of six atmospheres. This is conveyed through line 4I to 4tower15, and is expanded at expansion valve 1I prior to its introductionthereinto at 14. Tower 15 is provided with base coill y12 and head coil13 similar to coils 21 and 32 oi tower 35 and completely described invthat connection. The contents of line 43 or a portion of them may beby-passed through coil 12 for regulation of the A temperature .of thetower base, and all or a portion of them, after expansion through valve1I. may be by-passed through coil 13 for regulation of the tower headtemperature. As previously stated the by-pass connections for coil 1lhave been omitted from the drawing 'for purpose oi simplicatlon. Weoperate tower 15 at a pressure of live atmospheres andv maintain thereina head temperature of 0 C. and a base temperature of plus C. Thereby weeffect fractionation of the incoming stream and take off from the towerhead, through line 16, a mixture of propylene and propane, and from thetower base we take olf a residue of butylene and butane through line D.The butylene-butane fractionis conducted away through line D for furtherutilization as desired. J

Throughout the various fractionations in the process illustrated. we mayimprove the separation by discharging a portion of the more closelyseparated/product of one tower back to the head of the previous tower,to constitute an open reflux stream therein. Thus, a portion of theliquid product removed from the tower ,4D through the line 43 may bereturned through a line 80 having a pump 8l and a valvev 82 to the upperportion of the tower 35, to serve as a reflux and absorbing andconcentrating medium. By means of the valve 82 and a further valve B3located in the line 43, the proportions of the liquid withusual manner.

Similarly, a portion of the butane containing fraction removed from thebottom of the tower l 15 through the line D, may be delivered to thetower 40 as reflux. For this purpose, we provide a line 85 having avalve 86 and a pump 81 and communicating at one end with the line D andterminating at the other end in the upper portion of the tower 40. Anadditional valve 88 may be provided in the line D which with the valve85 may be employed for the purpose of regulating the proportion oftheliquid returned as reflux to the tower 40 and such excess liquid as mayb e withdrawn through the line D.

Throughout the various steps of our process for utilizing petroleumrefinery gas we can of course reduce the number of steps infractionating out a. cut containing any particular olefin when it doesnot disadvantageously ailect the usefulness of adjacent fractions orwhere, under the particular circumstances, the adjacent fraction is notto be used. Likewise, where it does not affect the usefulness ofadjacent fractions, we can fractionate to get the desired olefin as theprincipal scription that in our process refinery gases which 5 are to beseparated into twofractions relatively high and relatively lowrespectively in a lowboiling and refractory constituent, such as ethaneor ethylene, are introducedinto a fractionating tower, to the upperportion or which is-supplied `10 'as reflux a liquid freeorsubstantially freeV of such constituent and comprising, for example,`

butane and butylene.` The bottoms from this 'fractionating tower arethen subjected to a second fractionation for the purpose of removing anyconstituents absorbed by the reflux and the bottoms from the secondtower, thus stripped of said absorbed constituents, are returned atleast in part to the first fractionating'tower as a reriuxing andabsorbing medium. it being understood that the function of absorption isinherent inthe action of a liquid reflux. y Asa result of this absorbing4and stripping action, the overhead from the second tower issubstantially richer in high boiling and hence less refractoryconstituents. for example propylene and propane, than the overheadseparated from the first fractlonating tower.

It will further be understood that the proporf tions ofy any of theoleflns to the corresponding 30 paraiins (for example the proportion ofbutylene to butanel may vary considerably in accordance with theparticular gases initially fed to the process and that such gases maycomprise largely paramnic constituents, this `being largely a functionoi' the type of cracking operation from which the gases have beeninitially derived. Thus, where the gases are largely paraiiinic incharacter, the overhead from the tower 40 will comprise largely ethane,the overhead from the tower 15 will comprise largely-propane and theliquid effluent from thebottom of the tower 15 will consist largely oi'butane. In general however, both parainic and oleflnic constituents willbe present, as both paraiflnic and oleilnic constituents are found atleast to some extent in the gases resulting from all oil-crackingoperations.

The process of our invention is adapted to be employed wherever it isdesired to separate mixed hydrocarbon gases of the character indicatedinto ay plurality of fractions, such for example as an Aethane-ethylenefraction.. a propane-propylene fraction and a butane-butylene fraction.These various fractions, being different in character, may then beadvantageously subjected to different types of conversion operations, ormay be subjectedwto conversion operations maintained under diierentoptimum conditions according to thev natures of the individual fractionstreated. Thus, the ethane-ethylene fraction and the propane-propylenefraction may be utilized for the production of ethyl chloride and propylchloride, respectively, whereas the butane-butylene fraction maybesubjected to elevated temperature and pressure. with or without theassistance of suitable catalysts, in order to eifect the conversionthereofv to polymer gasoline.

Moreover, as has been indicated herein above, by reducing a number ofsteps inthe fractionation operation, we may similarly reduce the numberof fractions segregated. Thus, by conducting the operation in twostages, we may removemethane as overhead from the tower 25 and may thencomplete the fractionation in a second l tower'. withdrawing as overheadtherefrom a fraction comprising ethane, ethylene, propane and propylene.

It will be understood that our invention is not limited to theillustrative details set forth herein. but may variously be practicedand embodied within the scope of the claim hereinafter made.

What we claim is:

The process of recovering gases relatively free from low boilingparafiinic gaseous constituents such as ethane from hydrocarbon gasescontaining the same in addition to higher boiling nor: mally gaseousconstituents, which comprises introducing said gases in at least partlyliquefied form into a fractionating column, supplying to the upperportion of said column a reuxing andl scrubbing medium, removing fromthe upper portion of said column a gaseous fraction relatively rich insaid low-boiling paramnic gaseous constituents, removing from the lowerportion of said column a. liquid fraction, introducing the liquidfraction withdrawn from the first column the second column to the upperportion oi the iirst mentioned column to constitute the refluxing andscrubbing medium supplied thereto.

ERIC B. HJERPE. WILLIAM A. GRUSE.

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